Ars Technica is reporting that certain 64bit Mac models won't be able to run Mountain Lion. The problem is the graphic card drivers; these are still 32bit, and Apple is unwilling to update them to 64bit. A 64bit kernel can't load 32bit drivers, so that's that. Apple has a list of supported models on their Mountain Lion upgrade page, so you can easily check if your computer is capable of running Mountain Lion.

It's my only 68000 Mac. It now has a 500MB internal SCSI hard drive, 4MB RAM and triple boots System 6 from ROM, system 7.0 and 7.5.3 from Hard Drive. You can boot to System 6 at any point by cold restarting and holding down X and O (and possibly some of the modifiers, I forget) and it really does boot stupidly fast. I have no idea what the point of the ROM OS is, other than it being cool and requiring no working media drive to boot.

EDIT: another fun nugget of info, I installed 7.0 from Floppy, but 7.5.3 was from the CD image that Apple hosts. I downloaded it, mounted it on my 9500 and then installed on the classic over a local talk network... seriously!! Just a serial cable between two machines. Mind blowing.

I did have a 68000 Mac 2 at one point**, but I never turned it on and gave it away shortly after I got it. I do have a 6100/66 and a 9500/180MP (runs BeOS R5 and an unreleased Beta of R5.1) and a Beige Desktop G3/233 (10.3 is hacked on it with XPostFacto). I also have a Mac Mini with a Core i5 and a BlackBook (the late 2007 one, with Santa Rosa chipset, so unsupported by MountainLion.) I'd still have the 6100 running if only I could find the damn AAUI base10t adapter. That machine was sweet. My first Mac. I had it running MacOS 8.1 and System 7.5.3 at one point.

** I once got a tonne of Macs from eBay by losing an auction. The seller contacted me and told me the winning bidder only wanted the bundled software and sold me the G3, Mac 2, Mac Classic, Laserwriter 360Select and a tonne of manuals and software of £15. He was happy to see the back of it, I was happy to hord "treasure."

I also have one of those. 2MB of RAM, 8MHz 68000 and 40MB HD. I have it now on mostly MacMINIX use. Only problems are that Minix 1.5 lacked sockets and TCP/IP and the processor beign 8MHz 68000 makes compiling stuff "fun".